The present invention relates to an apparatus and a method for generation of a clock signal, i.e. an alternating signal having a constant frequency, in accordance with claim 1 and claim 9, respectively.
A signal generated in this manner offers, for instance, various applications in apparatuses and circuits, respectively, in which a time basis is required for certain time controls, (closed-loop) controls and/or measurements. A special application of such a time basis is the use in a so-called intelligent rechargeable battery. In these rechargeable batteries an intelligent component is integrated in form of a chip in which the previous history of the rechargeable battery, i.e., in particular, its current charging state, its maximum charging capacity and so on are stored. When during the process of the charging of the rechargeable battery its previous history and charging parameters are known then a, substantially more effective, i.e., in particular, faster and more complete, recharging of the rechargeable battery is possible.
For obtaining the previous history of the rechargeable battery such a chip requires a time basis in order to accurately sample the time behavior of the charging and discharging processes. As classic circuits for generation of a signal useable as a time basis and a clock signal, respectively, for instance conventional RC oscillators are known which generate an unattenuated electric oscillation having a certain curve shape and frequency having a constant amplitude. However, such RC oscillators comprise a relatively high temperature coefficient so that a high constancy of the frequency of the output signal and thereby a high accuracy of the corresponding time basis cannot be achieved in the case of variations of temperature and have a relatively high consumption of current which is disadvantageous, in particular, in the application in intelligent rechargeable batteries. In order to increase the constancy and accuracy, respectively, of RC oscillators these are often trimmed using additional oscillation circuits.
A further known possibility for generation of a time basis is the use of quartz oscillator. A quartz oscillator distinguishes itself particularly by its high constancy in frequency and its low temperature coefficient. However, such quartz oscillators are, in general, relatively expensive and relatively big. Moreover, the high accuracy of a time basis generated by a quartz oscillator is not necessarily required with some applications such as also with intelligent rechargeable batteries.
Further, in the prior art so called VCO""s (voltage controlled oscillator) are known. The VCO is a voltage-frequency converter and substantially consists of an integrator and a trigger. The frequency of the output signal of the VCO is proportional to the control voltage of the VCO. However, the VCO also comprises a high temperature coefficient for the output frequency so that with variations of temperature no time basis can be ensured having a sufficiently high accuracy.
Starting from the afore-mentioned prior art it is an object of the present invention to provide an apparatus and method for generation of a signal having a constant frequency with which the above-mentioned disadvantages of the prior art are avoided. In particular, an apparatus and a method for generation of a signal having a constant frequency shall be provided which comprise a sufficiently high constancy of frequency and a low temperature coefficient with relatively little space requirements and relatively little power consumption.
In accordance with the present invention this object is solved by an apparatus and a circuit, respectively, comprising the features of claim 1 and by a method comprising the features of claim 9.
The VCO for generation of a clock signal is according to the invention integrated in a (closed-loop) control circuit such that the frequency of its output signal is only determined by the circuit elements comprised in the (closed-loop) control circuit and having a low temperature coefficient These circuit elements are preferably an external current source and a capacity (or capacitance or capacitor) which can alternately be connected to an integrator circuit with the frequency of the clock signal wherein the output signal of the integrator circuit is fed to the VCO.
Particularly advantageous variations and further embodiments of the present invention are the subject-matter of further dependent claims.
The invention as well as further objects, features, advantages and applications thereof will be described in more detail in the following taking reference to the appended drawings. Therein all described and/or illustrated features taken alone or in any sensible combination form the subject-matter of the present invention independent of their summary in the claims or the dependencies thereof. In the drawings show: